Hubble provides the most accurate measure of the expansion of the universe to date

By analyzing more than thirty years of data collected by the Hubble Space Telescope, NASA was able to obtain the most accurate measurement to date of the rate of expansion of the universe. To operate them, the researchers calibrated more than forty “kilometer markers” of space and time.

Imagine a chocolate muffin in an oven. The lumps then move away from each other as the cake develops. If you could sit on one of these nuggets, then you could see all the others slipping away from you. In the Universe, it’s a bit the same.

Astronomers have known for almost a century that the universe is expanding. The farther away the galaxies are, the faster they travel. The speed at which they move relative to their distance from the Earth is defined as Hubble constantly. The measurement of this value was also one of the main tasks of the telescope.

To measure the Hubble constant, astronomers analyze the distances between different types of objects whose brightness is well known. For relatively dense objects, astronomers trust cepheids. They are a class of stars that pulsate in a predictable pattern. For larger distances, light off type Ia supernovaecosmic explosions of white dwarfs with a well-defined peak brightness.

A more accurate constant

Over the last few decades, measurements of these objects have allowed astronomers to calculate the Hubble constant of approx. 70 km per second per. megaparsek (/ s / Mpc). Note that a galaxy one megaparsec (about 3.3 million light-years) from Earth will move away at about 70 km per second, and that this speed increases by 70 km / s for each megaparsec away.

In recent years, however, teams have used other methods to try to refine this estimate, and the results have varied widely. For this new work, a NASA team compiled and analyzed the most complete catalog of these objects to date (cepeids and type Ia supernova) to make the most accurate measurement yet of this constant. All these objects, isolated in forty-two galaxieswas pictured by Hubble above last thirty years.

Based on this work, the Hubble constant was what the team calculated 73 km / s / mpc, at plus or minus 1 km / s / Mpc. This brings the uncertainty down to just 1.4%, which is more accurate than other measurements. This new refinement could thus help astronomers improve the models of cosmology and thus make it possible to better specify its age or its future fate.

Abell 2261 galaxy cluster photographed by Hubble. Credits: NASA, ESA, M. Postman (STScI), T. Lauer (NOAO) and the CLASH team

A big hole that questions

A great mystery remains, however. The rate of expansion of the universe was predicted to be slower than what Hubble actually sees. By combining the standard cosmological model of the universe with measurements from the European Space Agency’s Planck mission (which observed the background radiation from the Big Bang 13.8 billion years ago), astronomers predict a lower value for the Hubble constant: 67.5 km / s / Mpc.

According to the researchers, given Hubble’s large sample size, there is only a one-in-a-million chance that astronomers are mistaken about the new estimate. However, the measurement of the Standard Model of Cosmology is also very strong. Astronomers still lack an explanation for the interruption between the expansion velocities of the local universe and the early universe, but the answer could involve new physics.

The answer to this mystery may come to us with the James Webb Telescope, which will expand Hubble’s work by isolating cosmic markers at greater distances or with sharper resolution.

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